Lu Guang, a three-time World Press Photo award winner, had been invited to take part in photography events in the regional capital, Urumqi, in late October, his wife, Xu Xiaoli, said in online posts.

She lost touch with her husband on Nov. 3 while he was travelling alone in the southern city of Kashgar and has not heard from him since, Xu said.

She later contacted the wife of the person who invited her husband to Xinjiang and was told both men had been taken away by state security officers, Xu said.

The Xinjiang regional government did not immediately respond to a request for comment.

At a regular news briefing in Beijing, Chinese foreign ministry spokesman Geng Shuang said he was not aware of the case.

“He went to Kashgar alone,” Xu, who lives in New York City, told Reuters on Tuesday. “Later, it was both him and the friend who were taken away.”

Lu’s prize-winning work has largely focused on sensitive environmental and social issues in China, including industrial pollution, drug addiction and people living with AIDS.

Beijing has faced an outcry from activists, academics, foreign governments and U.N. rights experts over mass detentions and strict surveillance of the ethnic Uighur minority and other Muslim groups in Xinjiang. [nL4N1Y22XF] [nL8N1VL3XL]

Chinese authorities routinely deny any ethnic or religious repression in Xinjiang and say its measures are needed to combat the influence of religious extremism.

Xu said she had not received any official notice of Lu’s detention and had been unable to contact Xinjiang police.

“Dec. 4 is our 20th wedding anniversary. He was meant to celebrate with us together,” Xu said in an online post.

“Ever since I lost touch with him, the days have dragged on like years.”